DirectCPviolation inB→Xsγdecays as a signature of new physics

Abstract

We argue that the observation of a sizable direct $\mathrm{CP}$ asymmetry $A_{\mathrm{CP}}^{\overrightarrow{b}s\gamma }$ in the inclusive decays $\overrightarrow{B}{X}_s\gamma$ would be a clean signal of new physics. In the standard model, $A_{\mathrm{CP}}^{\overrightarrow{b}s\gamma }$ can be calculated reliably and is found to be below 1% in magnitude. In extensions of the standard model with new $\mathrm{CP}$-violating couplings, large $\mathrm{CP}$ asymmetries are possible without conflicting with the experimental value of the branching ratio for the decays $\overrightarrow{B}{X}_s\gamma .$ In particular, large asymmetries arise naturally in models with enhanced chromomagnetic dipole operators. Some generic examples of such models are explored and their implications for the semileptonic branching ratio and charm yield in $B$ decays discussed.